The Soul Sirens are a class of Kamina that are able to manipulate souls into objects or weapons. By harvesting a soul from a creature or person, they can use its power to temporarily conjure an object or weapon. The soul is then released and the conjured object or weapon disappears once it has served its purpose. A Soul Siren can summon multiple objects, but the object's shape is dependant on the soul's nature.
This is a practised ability among the Kamina - however, it is against their laws to harvest a soul from a living being or creature. The Soul Sirens are only ever allowed to harvest a soul that has already passed on, by using a simple ritual to call upon a soul from their place of eternal rest, known as - ‘The Embrace’.